Dynamic failure of brittle materials is a rather complex issue. In this paper, experimental work was carried out for plaster model, to study the crack development features of brittle materials under the action of explosion. It shows that couple medium has great influences on detonation wave type. The water has the cushioning effect on detonation wave, which makes the wave crest truncated and results in low wave amplitude and large wave width. Detonation wave type has apparent influence on failure features of brittle materials, of which larger wave width would keep the wall of exploded hole intact and increase the development length of cracks. The research results would be applied to coal mining to increase the efficiency of gas pumping drainage.